1. Field of the Invention
The subject matter of this invention relates generally to auxiliary contact interlinkage mechanisms for circuit interrupter apparatus in metal-clad switchgear. The invention relates more particularly to fail-safe interlinkage apparatus.
2. Description of the Prior Art
Metal-clad switchgear for removable main circuit breakers is well known in the prior art. Examples of such switchgear may be found in the following U.S. Pat. Nos. 2,443,669, issued June 24, 1948 to R. S. Tusing; 2,921,998, issued Jan. 19, 1960 to Pokorny et al; 3,710,044, issued Jan. 9, 1973 to Sharp; 3,767,874, issued Oct. 23, 1973 to Wilson; 3,770,917, issued Nov. 6, 1973 to Tjebben; 3,793,493, issued Feb. 19, 1974 to Wilson, 4,002,864, issued Jan. 11, 1977 to Kuhn et al; and 4,002,865, issued Jan. 11, 1977 to Kuhn et al. All of the above patents teach metal enclosed or metal-clad switchgear apparatus for use with draw-out circuit breakers which may be levered into position or otherwise disposed in a metal-clad switchgear cabinet for operation. Usually a levering-in or racking-in device with associated and appropriate safety interlocks are taught. It is also known to utilize auxiliary contacts in association with the main interrupter contacts of metal-clad switchgear apparatus. The auxiliary contacts usually perform indicating or control functions and are not meant to carry the main load current, but are meant to open and close in some direct correspondence with the opening or closing of the main circuit interrupter contacts. In some cases the auxiliary contacts are opened and closed in direct conjunction with the opening and closing of the circuit interrupter contacts and in other cases they are not. In cases where the auxiliary contacts are mounted as part of the metal-clad cabinet rather than on the circuit interrupter itself it is necessary to provide an interlinkage between the circuit interrupter and the auxiliary contacts when auxiliary contact operation is desirable. Almost always it is desirous to actuate the auxiliary contacts when the main circuit breaker is in the operating position. In other instances it is sometimes desirous to operate the auxiliary contacts for test purposes. An example of the latter occurs when the circuit breaker apparatus is withdrawn away from the main high voltage terminals of the metal enclosed cabinet to a test position therein where opening and closing of the main contacts can be accomplished without affecting the external circuit which is connected from the main circuit breaker. Such an apparatus is shown in an instruction booklet entitled "Instructions for Porcel-Line Metal-Clad Switchgear Type DH-P Housings Indoor and Outdoor" identified by the reference symbol I.B. 32-253A effective September 1967. FIG. 23 of the latter booklet and the description on page 11 and 12 thereof given an adequate description of a prior art mechanism-operated cell switch (M.O.C. switch). In this case a pin on the circuit interrupter is disposed in a channel which is attached to a pantograph which in turn is connected by way of a long rod to the auxiliary contacts. As the circuit breaker is moved from the test position to the operating position and vice versa, the pin traverses the length of the channel always remaining in a position to move the channel and thus the pantograph and auxiliary contacts when the circuit breaker mechanism is operated. Furthermore, a refinement of the latter apparatus is shown in FIG. 1 of the present application in which one slidable two-position channel is disposed inside of the main channel. With such an apparatus the auxiliary contacts will always operate in conjunction with the operation of the main circuit interrupter when the main circuit interrupter is in the operating position. When the main circuit interrupter has been withdrawn to the test position the pin clears the channel and will not cause operation of the auxiliary contacts in conjunction with the operation of the main contacts unless the slidable channel is advanced forward to a second position in which case it recaptures the pin. Consequently, when the circuit breaker apparatus is in the test position operation of the auxiliary contacts is selectable. It is through that, the previously described apparatus represents the known extent of the prior art. However it presents a disadvantage, namely, one of safety. As the main circuit interrupter is levered into the operating position once again and then withdrawn to the test position a previous selection for the slidable channel may maintain the slidable channel in such position as to cause actuation of the auxiliary contacts when the main contacts are operated. This may not always be desirable on subsequent operations of the circuit breaker apparatus. Consequently, it would be highly desirable to provide a fail-safe feature wherein when the circuit breaker apparatus is levered in, the slidable channel would always be placed in a first operating position so that a subsequent removal or withdrawal of the circuit breaker apparatus to the test position will not cause actuation of the secondary contacts unless the selectable channel is then deliberately moved to the test position.